One image forming device known in the art includes a temperature sensing member for sensing the temperature of a heating body, and a control unit for controlling a power supply unit to supply power to the heating body based on the detection results by the temperature sensing member (Japanese Patent Application Publication No. 2004-271905, for example).
However, this conventional image forming device does not monitor the state of power output from the power supply unit. Therefore, if the state of power output from the power supply unit changes from a normal state to an abnormal state during a print control process due to a malfunction in the temperature sensing member, the control unit would not detect this abnormal state and the malfunction in the temperature sensing member.